The present invention broadly relates to gear pitch testing machines and, more specifically, pertains to a new and improved construction of and method of employing an inspection or measuring machine for measuring the circular pitch spacing of teeth on a gear.
Generally speaking, the inspection or measuring machine of the present invention for measuring the circular pitch spacing of teeth on a measurement-circle of a gear comprises a measurement sensor having a mechanically pre-loadable feeler or contact arm capable of being deflected by a flank of a tooth of the gear being measured, having an active sensing range with a range of linear response and generating an output signal defining a linear measurement value; a first transport carriage translatably drivable in a direction substantially radial to the gear for mounting the measurement sensor; drive means for rotating the gear; angular displacement sensing means capable of being operatively connected to the gear; wherein the angular displacement sensing means generates a pulse signal when the measurement sensor enters its range of linear response; and a control processor is connected to the angular displacement sensing means for controlling measurement operations and for computing measurement values.
The method of inspection of the present invention measures the circular pitch spacing of teeth on a measurement-circle of a gear by means of a measurement-sensing means or sensor having a feeler or contact arm capable of being deflected by a flank of a tooth of the gear being measured and having a range of linear response and being translatable at least in a direction substantially radial to the gear and having an inherent systematic error factor and by means of an angular displacement sensing means generating signal pulses corresponding to an angular displacement of the gear.
An inspection machine of this type in which the gear being measured turns continuously is known from the German Pat. No. 3,125,929 granted Mar. 24, 1983. This known inspection machine is only suitable for the measurement of internal and external gear teeth of small gears, since the measurement becomes increasingly inaccurate as the radius of the measurement-circle increases due to the limited resolution of the angular displacement sensing means. Although the angular displacement sensing means of this known device employs a graduated scale of the highest possible resolution and each line of graduation generates a signal pulse, if the diameter of the gear to be tested is considerably greater than the diameter of the angular displacement sensing means, motions of the measurement sensing feeler or contact arm can take place between two such graduation lines and therefore not be measured since the counters of the inspection machine only employ a count of pulses generated by the graduation lines for determining the angular displacement measurement value.
The following equation defines the measurement-uncertainty of this known device in relation to the measurement radius r: ##EQU1## where:
t.sub.s is the spacing of the graduation lines in millimeters of arc-length;
r is the measuring radius in millimeters;
r.sub.w is the radius of the graduated circular disc of the angular displacement sensing means in millimeters;
.sigma..sub.a is the sensing-uncertainty of the graduation line spacing and random errors of the mechanical components in radians (independent of the angular displacement sensing means, of the method of sensing the same and of the mechanism devoted to measuring angular displacement);
.phi..sub.i is the angular displacement in radians;
K is a constant factor or coefficient (dependent upon the measurement sensing means and upon the rotary work table upon which the gear is mounted) (dimensionless).
The total measurement-uncertainty U.sub.r is composed of the random errors A and B as well as the systematic error E. All of these errors increase linearly with the measurement radius r.